Reply to Levis and Rendini

Luteolin as a potential host-directed immunotherapy adjunct to isoniazid treatment of tuberculosis

Tuberculosis (TB) remains a major health problem throughout the world with one third of the population latently infected and ~1.74 million deaths annually. Current therapy consists of multiple antibiotics and a lengthy treatment regimen, which is associated with risk for the generation of drug-resistant Mycobacterium tuberculosis variants. Therefore, alternate host directed strategies that can shorten treatment length and enhance anti-TB immunity during the treatment phase are urgently needed. Here, we show that Luteolin, a plant-derived hepatoprotective immunomodulator, when administered along with isoniazid as potential host directed therapy promotes anti-TB immunity, reduces the length of TB treatment and prevents disease relapse. Luteolin also enhances long-term anti-TB immunity by promoting central memory T cell responses. Furthermore, we found that Luteolin enhances the activities of natural killer and natural killer T cells, both of which exhibit antitubercular attributes. Therefore, the addition of Luteolin to conventional antibiotic therapy may provide a means to avoid the development of drug-resistance and to improve disease outcome.

The current TB therapy is lengthy, expensive, and may induce severe hepatotoxicity in patients, often leading to premature withdrawal from therapy, which is associated with the risk of generating drug-resistant strains. We considered inclusion of a hepatoprotective immunomodulator, Luteolin, as a potential host directed adjunct to available therapy as a means to improve its efficacy by enhancing host protective immunity. Luteolin-Isoniazid combination therapy induces improved central memory T cell responses. The boosted immune responses permitted reduction of treatment duration, improved treatment outcome and efficiently prevented disease relapse. Luteolin treatment rendered the host resistant against reinfection and reactivation of the disease, which is a major challenge following conventional TB treatment. We conclude that Luteolin is an effective adjunctive immunomodulator for designing anti-TB immunotherapeutics that can provide superior host protection.

Luteolin-mediated Kv1.3 K+ channel inhibition augments BCG vaccine efficacy against tuberculosis by promoting central memory T cell responses in mice

Despite the availability of multiple antibiotics, tuberculosis (TB) remains a major health problem worldwide, with one third of the population latently infected and ~2 million deaths annually. The only available vaccine for TB, Bacillus Calmette Guérin (BCG), is ineffective against adult pulmonary TB. Therefore, alternate strategies that enhance vaccine efficacy are urgently needed. Vaccine efficacy and long-term immune memory are critically dependent on central memory T (T_CM) cells, whereas effector memory T (T_EM) cells are important for clearing acute infections. Recently, it has been shown that inhibition of the Kv1.3 K⁺ ion channel, which is predominantly expressed on T_EM but not T_CM cells, profoundly enhances T_CM cell differentiation. We exploited this phenomenon to improve T_CM:T_EM cell ratios and protective immunity against Mycobacterium tuberculosis infection in response to BCG vaccination of mice. We demonstrate that luteolin, a plant-derived Kv1.3 K⁺ channel inhibitor, profoundly promotes T_CM cells by selectively inhibiting T_EM cells, and significantly enhances BCG vaccine efficacy. Thus, addition of luteolin to BCG vaccination may provide a sustainable means to improve vaccine efficacy by boosting host immunity via modulation of memory T cell differentiation.

Bacillus Calmette Guérin (BCG) is not effective against adult pulmonary tuberculosis (TB). Inhibition of the Kv1.3 K⁺ ion channel by the antibiotic clofazimine has been shown to enhance BCG-induced immunity. However, clofazimine has limited efficacy and is associated with substantial side effects in treated patients. Therefore, we explored alternatives to clofazimine. Luteolin is a plant-based flavonoid that inhibits Kv1.3. We show that administration of luteolin during BCG vaccination enhances antigen-specific immunity by promoting the T central memory (T_CM) cell pool, which is critically important for long term host protection. Consequently, luteolin-mediated immune modulation enhances vaccine efficacy. As luteolin is a biologically safe food supplement, it could be easily applied during vaccination.